Banning a book can go like this: An outraged parent complains about a book to the school librarian or principal. After a noisy debate, the school administrators decide that the book should be removed from circulation. Or, banning a book can go like this: A librarian receives a new book. Perhaps it shows LGBT issues or atheism in a sympathetic light. Perhaps it portrays civil rights struggles in a way that might offend some local sensibilities. Whatever the reason, she quietly puts the book in a back room. Then she politely discourages questions about it.
